The present invention relates to a brake actuator in an air brake system. More specifically, the present invention relates to a parking brake actuator with a parking brake spring.
Parking brakes that operate with a spring to actuate the brake include a parking brake diaphragm that moves when air flows in and out of the parking brake chamber. Air enters the release volume of the parking brake spring chamber and the expansion compresses the brake spring during the parking brake “release” cycle. During the parking brake “apply” cycle air exits the release volume of the parking brake spring chamber and the spring volume of the parking brake spring chamber increases as the spring extends.
Many conventional brake actuators are open to the environment. These brake actuators have multiple internal components that are vulnerable to contamination in the applied position. Contamination of the spring volume causes corrosion of the power spring and other internal components, eventually causing brake chamber failure.
Other conventional brake actuators are configured to allow air out of but not into the spring volume of the brake spring chamber to minimize or eliminate the possibility of contamination of the components. However, during operation of actuators which are sealed in this manner, a vacuum can develop as the parking brake is applied and the spring volume within the brake spring chamber increases. The vacuum created during the brake apply cycle works against the brake actuator's delivery of full parking force for the particular spring type and spring stroke of the brake actuator. Thus, it would be beneficial to improve the brake actuator's delivery of full parking force while also preventing contamination inside the brake actuator.